The present invention relates to a color image reading apparatus used for a digital color copying machine or the like, and more particularly to a color image reading apparatus employing a CCD linear image sensor.
For reproducing a color image, signals of each color of R, G and B need to be processed. In this case, when a CCD line is provided for each color, the number of pixels of the CCD is caused to be large and the composition is thereby caused to be complex, though the signal processing is simple. Therefore, it is required that the structure of a CCD linear sensor is simplified while the high image quality is kept.
With the background mentioned above, inventors of the invention have devised a linear sensor shown in FIG. 3 and studied for utilizing it to practical use.
The CCD linear sensor mentioned above has pixel rows equivalent to two lines in the sub-scanning direction, and one row of them is provided with green filters, and the other is provided with red filters and blue filters each being arranged alternately, and row of each sensor is deviated to that of another by 1/2 pixel. Owing to the arrangement wherein red pixels and blue pixels are placed alternately, the number of pixels can be reduced, which is an advantageous point. The reason why green pixels equivalent in number to one line are prepared is that green has more influence on eyes of a human being and it has an influence on reproduction accuracy for brightness information.
In the linear sensor, however, there is a difference of reading density between red and blue pixels and green pixels. Therefore, when output signals of each sensor row are processed without being treated, the reproducibility is deteriorated and high image quality can not be expected. It is therefore necessary to create a method for preparing one unit of data by combining output signals of each pixel, and to realize the function of the method.
The invention has been devised based on the above-mentioned consideration, and its object is to attain high image quality of a color image reading apparatus employing a color CCD linear sensor whose structure is simplified.